in PJL, you can associate (link) deliverables with the project acitivities and have the status rolling up (only if you have one delivrable per activity). That is a very good functionality.
However, during the creation of the project, the creator must take the decision if only one delivrable can be associated to the project or not.
That is, when the decision is taken, it cannot be changed. As a consequence if you believe you do not need more than one delivrable per activity and benefit of the automatic roll up, if one activity happens to need more than one deliverable you can do this.
The idea is to provide more flexibility
allow roll up status (from delivrable to activity) for activities having more than one delivrable
allow to have in the same project activities either with one delivrable or more.
In other words, there should not be such option at the creation of the project. One could always be able at any time to link as many deliverable as required in an activity and the roll up will logically be from the sum of the status of the delivrable to the activity (other way round will not work).
Please let me know what you think
PS: This is based on 9.1 experience. if 10.1 already does that, please let me know and I'll remove the idea,